1. Field of the Invention
The invention relates to an exhaust component or an exhaust device, having at least two inlet lines for connection to an internal combustion engine and a wall.
The exhaust component is used as part of an exhaust system of an internal combustion engine for conducting and possibly catalytically treating and cleaning exhaust gas. The internal combustion engine may, for example, be a gasoline engine of a passenger automobile or other roadgoing motor vehicle.
2. Description of the Prior Art
Known exhaust manifolds have two or more inlet lines which can be connected to an internal combustion engine, and a collection outlet which is common to these inlet lines, the various lines comprising pipes with simple metal walls. During operation of the internal combustion engine, such walls are heated to high temperatures, normally of at least about 700xc2x0 C., so that such exhaust manifolds, and in particular their inlet lines, emit large quantities of heat to their environment. The considerable amounts of heat, which are emitted by radiation, thermal conduction and convection, cause undesirable heating of temperature-sensitive parts and/or spaces which are arranged close to the exhaust manifold, such as for example electrical components, electronic components and/or components which contain plastic, the fuel tank, a spare wheel and/or the passenger compartment. In practice, therefore, it is often necessary to arrange heat-shield plates in the vicinity of the exhaust manifold, which plates increase the costs involved in the production of the vehicle, take up large amounts of space and, owing to the vibrations generated by the engine, may cause noise problems.
Furthermore, it is known to surround the gas-carrying parts of an exhaust manifold or catalytic converter with a double-walled cooling jacket. The latter had an intermediate space, through which water is guided during operation. However, a cooling jacket of this nature additionally requires a cooling installation in order to circulate and cool the water which has been heated in the cooling jacket, or requires an increase in the size of a cooling system which serves primarily to cool the engine. This increases the space which is take up and the costs.
U.S. Pat. No. 3,751,920 has disclosed a non-catalytic exhaust reactor having a casing and inlet lines which, at locations which are distributed along the cylindrical casing jacket, open through this jacket into the interior space of the casing. This exhaust reactor thus does not form an exhaust manifold and, during operation, produces considerable back-pressure. The inlet lines of the exhaust reactor evidently have metal walls and thus emit large amounts of heat to the environment. The jacket has an outer wall which is evidently made from metal. This outer wall surrounds an insulating layer which, at the openings of the inlet lines and at the outlet line, is provided with holes and, on the inside, on the outside, at the ends and at the position of the holes is provided with coatings. Insulating layers are also arranged on the inner sides of the end walls. These insulating layers and their coatings therefore have to be produced and fitted in addition to the metal, cylindrical outer wall, the metal, planar end walls and the inlet lines. Therefore, a large number of separate parts have to be produced and assembled in order to form this casing, the inlet lines and the insulating layers. It should be noted that the materials of which the insulating layers and coatings consist are not specified.
French patent disclosure 2,238,585 has disclosed a composite material which comprises a glass fiber fabric which is arranged between two metal sheets and is used in particular to form muffler casings. To produce such a casing, two sheets of the composite material are shaped into half-shells and are then joined together at edges. French patent disclosure 2,238,585 does not disclose an exhaust manifold. Furthermore, the glass fiber fabric which is disclosed which is only relatively thin, and, in addition, has only a low compressive strength. However, considerable compressive forces have to be applied to a planar, composite sheet in order to deform the sheet into an exhaust manifold which has relatively small radii of curvature, and consequently the glass fiber fabric would be compressed to a very considerable extent. According to tests carried out, the thickness of the glass fiber fabric in the finished exhaust manifold would probably amount to at most about 20% to 35% of the original thickness and would then be only less than about 1 mm. Consequently, the heat emitted by an exhaust manifold could only be reduced to an insufficient extent.
U.S. Pat. No. 4,215,093 has disclosed a catalytic converter and two inlet lines for connecting an internal combustion engine to the catalytic converter. The latter has a casing with two walls, each of which is composed of two shells and between which there is an intermediate space which contains air. However, the inlet lines only have simple metal walls which, during operation, are heated to high temperatures and emit large quantities of heat. Furthermore, tests carried out on catalytic converters in passenger automobiles with a similar double-walled casing have shown that the outer wall of such casings, during operation, is heated to high temperatures despite the intermediate space which contains air, these high temperatures typically amounting to about 500xc2x0 C. to 600xc2x0 C. Accordingly, a catalytic converter of this nature also emits large amounts of heat to its environment. The exhaust system which is known from the U.S. Pat. No. 4,215,093 also exhibits the disadvantages that it is necessary to assemble a large number of separate parts in order to produce it, thus making production of the exhaust system more expensive. Furthermore, the connection between the shells which form the outer wall by means of screws requires large amounts of space.
Similar problems may also arise in the case of a separate exhaust manifold.
The invention is therefore based on the object of providing an exhaust component or an exhaust device for conducting and possibly catalytically treating and cleaning exhaust gas which eliminates the drawbacks of known exhaust components and/or exhaust devices having an exhaust manifold and/or catalytic converter with at least two inlet lines and produces good thermal insulation but can nevertheless be produced and fitted at low cost and takes up only small amounts of space.
According to the invention, this object is achieved by means of an exhaust component having at least two inlet lines for connection to an internal combustion engine and a wall, wherein the wall has two wall elements, each with two metal shells and a layer of heat-insulating material which is located between these shells, and wherein the two wall elements have edge sections which are connected to one another and together, in cross section, surround interior spaces of all the inlet lines.
The invention furthermore relates to a method for producing an exhaust component having at least two inlet lines for connection to an internal combustion engine and a wall comprising two wall elements, each with two metal shells and a layer of heat-insulating material which is locacted between these shells, the two wall elements having edge sections which are connected to one another and together, in cross section, surround interior spaces of all the inlet lines, wherein two sheet-metal parts are provided for each wall element, each of which sheet-metal parts serves to form one of the shells, wherein a layer of heat-insulating material is arranged between the two sheet-metal parts, and wherein the two sheet-metal parts and the layer arranged between them are then together deformed in such a manner that the two wall elements together, in cross section, surround interior spaces of the inlet lines.
The layer of heat-insulating material which, according to the invention, is present between the shells of each wall element produces good thermal insulation. This ensures that the heat supplied from the exhaust gas substantially remains within the exhaust gas and/or within the interior of the exhaust component or the exhaust device. The heat which remains in the exhaust gas is conveyed onwards by this gas and is at least to a large extent dissipated into the environment together with the exhaust gas. Each outer shell of the exhaust component or of the exhaust system, in operation, is therefore heated only to a relatively low temperature. Furthermore, the exhaust component emits only small amounts of heat to its environment. Accordingly, it is also unnecessary to protect heat-sensitive parts or spaces which are located in the vicinity of the exhaust component from the heat, which is radiated from the exhaust component or is emitted in some other way, by means of heat shields.
In an advantageous configuration of the exhaust component, it has an exhaust manifold and a catalytic converter which forms a single unit with the exhaust manifold and contains catalyst means for the catalytic treatment of exhaust gas. The two wall elements of the exhaust manifold may then, by way of example, in cross section also completely surround an interior space of the catalytic converter and, in particular, the catalyst means. Alternatively, two additional wall elements may be provided for the catalytic converter each of which wall elements has two metal shells and a layer of heat-insulating material arranged between these shells. The two additional wall elements may then together, in cross section, completely surround the catalyst means and may be connected, for example directly, indirectly, securely and tightly to the wall elements which belong to the exhaust manifold. This design of the exhaust component also provides very good thermal insulation of the catalytic converter and its connection to the exhaust manifold. Furthermore, a unit of this nature can be produced particularly economically.
The wall elements are preferably of strong and essentially rigid design, and are connected to one another rigidly and at least approximately, or completely, tightly, in such a manner that they are self-supporting and together form a self-supporting part of the wall. At least a substantial part of the wall of the exhaust component may then comprise exclusively the wall elements which are connected to one another. The wall then only has to be provided with connection means at most, for example, at the inlet and/or the outlet of the exhaust component, in order to connect the exhaust component to the internal combustion engine and a part of the exhaust system which is arranged downstream of the exhaust component. The connection means may, for example, have one connection flange which is common to all the inlet lines or at least two connection flanges which are assigned to different inlet lines. Furthermore, the wall elements may then, at least for most of the wall, form the outer limit of the exhaust component.
The wall elements may be designed and connected to one another in such a manner that they take up only small amounts of space. The shells are, for example, from about 0.5 mm to 1 mm thick. In the finished exhaust component, the heat-insulating layer is preferably generally at most 10 mm, preferably essentially at least 2 mm and, for example, at least,approximately 3 mm and at most 5 mm thick. The temperatures of the outer shells of the wall elements are then, for example, at most approximately 50% of the temperature, measured starting from 0xc2x0 C., of the exhaust gas and/or of the temperatures which would arise on the outer surface of a simple metal wall with an otherwise identical design of the exhaust component or of the exhaust device.
The heat-insulating material is preferably inorganic, noncombustible and is able to withstand heat at least up to the operating temperature of the exhaust component and to the temperature of the exhaust gas, for example up to at least 800xc2x0 C. Each layer of insulating material comprises, for example, a cohesive, microporous plate and/or sheets which have at least a certain strength, in particular a relatively high compressive strength. In this context, xe2x80x9cmicroporousxe2x80x9d means that the layer or plate has pores with a size of approximately 1 xcexcm or a few xcexcm, but less than 10 xcexcm, or even less than 1 xcexcm. Each heat-insulating layer is formed, for example, from a material which was originally in particle form and at least mainly comprised grains, possibly with the addition of fibers, and was consolidated by compression and by a heat treatment and/or a chemical reaction. Therefore, each such layer contains, for example, grains which are bonded more or less strongly together, and possibly also fibers which serve for reinforcement purposes. The fiber content is, for example, at most about 10% by weight, so that the layer or plate has a structure which is grained at least to a large extent, and for example for the most part. The insulating material and, in particular, its granular components comprise, for example, mainly oxidic substances. The insulating material contains, for example, silica and/or at least one silicate and/or oxide ceramics, preferably comprises at least 50% by weight of highly dispersed silica. The fibers comprise, for example, an inorganic and/or oxide/ceramic material. Such microporous insulating materials are described, for example, in the European patent disclosure 0,029,227 and the corresponding U.S. Pat. No. 4,985,163 and are commercially available for example, under the trade name WACKER WDS from Wacker-Chemie GmbH, Munich, Federal Republic of Germany.
To produce the wall, two sheet-metal parts which were originally planar may, for the or each wall element, be formed into shells and joined together. The two sheet-metal parts which serve to form a pair of shells may, at least for a large part of the forming operation, be deformed in pairs together with a layer of heat-insulating material which is arranged between them. This allows economic manufacture of the wall.
The forming may, for example, be carried out by deep-drawing. During the forming operation, a considerable compressive force is exerted on the sheet-metal parts or shells and the layer of heat-insulating material arranged between them. In the process, the heat-insulating layer is compressed. If the heat-insulating material comprises a pre-consolidated, microporous plate or sheet, the thickness of the heat-insulating layer will only be reduced during forming by, for example, less than 50% in particular normally about 20% to 40%. Therefore, the thickness of the layer prior to forming only has to be relatively less great than in the finished exhaust component.
If appropriate, each heat-insulating layer may comprise, instead of a microporous plate or sheet, at least mainly a fibrous material, for example a single-layer or multilayer fabric. The fibers may, for example, comprise oxide ceramics and/or rock wool, basalt fibers, glass wool and/or any other inorganic material. However, fibrous material is compressed to a considerably greater extent during forming than a pre-consolidated, microporous plate or sheet, so that the thickness decreases by about 65% to 80%, for example, during forming.